The invention broadly relates to tire building machinery, and specifically to a device that is provided at each of the opposing ends of a tire building drum to engage and hold a pair of tire bead rings, in position, as the ply endings of one or more unvulcanized carcass plies, layered on the drum, are turned up and reversely wrapped around the bead rings to anchor the bead rings firmly to canvass plies to form an unvulcanized tire carcass to which are added the unvulcanized rubber tread and sidewalls for subsequent molding and vulcanization.
Such devices are well known and normally comprise a plurality of similar, bead lock segments which are equally arcuately spaced about the longitudinal center axis of the tire building drum, adjacent opposing ends of the outer cylindrical shell of the drum on which the unvulcanized tire carcass is built. The segments are simultaneously reciprocal in radial directions to and from the center axis of the tire building drum.
U.S. Pat. No. 4,087,306 shows and describes a typical tire building drum that employs annular, inflatable air bags for operating the bead lock segments, in unison. U.S. Pat. No. 4,007,081 discloses the use of a complex linkage system for regulating the movement of the bead lock segments. U.S. Pat. No. 3,871,942 discloses a rack and pinion drive to operate the bead lock segments and move them in radial directions to and from the center axis of the drum. The invention of this application is directed to a totally different mechanism for controlling the movement and operation of the set of bead lock segments that are at each end of the cylindrical, outer shell of a tire building drum.
Briefly stated, the invention is in a tire building drum that employs adjacent each of its opposing ends, a set of bead lock segments with bead seats that are in circumferential alignment around the center axis of the drum. Means are provided for slidably mounting the segments of each set, for reciprocating movement along fixed radial raceways or pathways to and from the center axis of the drum. A scroll member is mounted adjacent each set of bead lock members for rotation in either direction about the center axis of the drum. Means are supplied to operatively connect the scroll members and adjacent bead lock segments, so that the segments will move, in unison and equal distances, along the radial pathways in response to rotation of the scroll member, such means including cam rollers moveable along a trackway that spirals in helical fashion around the center axis of the drum.
The spiral of the trackway is such that a minimum of effort or force is required to move the segments radially to and from the center axis of the drum.